Loose Sapphires: Corundum is the mineralogical name for aluminium oxide. It is impurities that
combine with aluminum oxide that create the beautiful color varieties of Corundum pictured above.
Sapphires - Coloration
Corundum can be colorless, blue, black, brown, orange, yellow, green, indigo, violet, pink, or red. However, as
noted above, red corundum is called ruby, while pink corundum is referred to as Pink Sapphire. Blue corundum
is most commonly simply called Sapphire. &mbsp;Other colors of corundum, except red, are also called
Sapphires, but usually with the color specified as a prefix to the word Sapphire, for example,
Yellow Sapphire.
Pure Corundum is colorless, often called white, and although quite rare, tends not to be valuable because it does not have
much brilliance. Colors, as in many gemstones, are caused by small amounts of impurity, usually metallic
oxides. This is a case where an impurity is desirable. Chromic oxide causes brilliant red coloring
in corundum, thereby producing Rubies. Ferric oxide causes yellow coloration, titanium oxide produces
vivid blue. However, the coloration of sapphires is not this straight forward. The titanium and iron are
usually present in the form of ilmenite, a mineral which is a titanium iron oxide, TiFeO3. Ilmenite is not
isomorphous with aluminium oxide. Isomorphous means being able to replace the host mineral within its crystal
structure. Instead, ilmenite is present as a microscopic inclusion, in the form of colloidal particles. This
colloidal nature may be responsible for other optical effects such as "silk", asterism (stars), and color banding.
Sapphires - Durability
Corundum is very hard, having a hardness of 9 on Moh's scale, compared with 10 for diamond,
and 8 for topaz. Hardness is generally a desirable feature is gemstones.
Sapphires - Sources
Originally, the best loose Sapphires and Rubies came from Burma, where they are believed to have been mined
possibly from prehistoric times. Certainly, they appear to have been worked during the times of Marco Polo.
Kashmir is another source of very fine sapphires, famous for its "Cornflower Blue" stones.
Thailand, previously called Siam, is an important source of beautiful sapphire.
The term "Ceylon" Sapphire is frequently used to denote pale to medium blue sapphires. Unless the
stone is known to originate from Sri Lanka, as it is now called, such sapphires should accurately be called
"Ceylon-type" Sapphire. Australia currently produces and dark variety of sapphire. For this
reason, the term "Australian Sapphire" is sometimes used to denote dark colored sapphires, similar to the way to
the term "Ceylon Sapphire" for lighter stones. Sapphires are also found in Montana and Colorado
in the USA, India, with small quantities being found in numerous other countries.
Sapphires - Pricing
The price range of Sapphires is very large, ranging from under a few dollars per carat
to many thousands of pounds per carat, depending primarily on color, but also on brilliance,
which is affected by clarity and cut.
Sapphires - Finest and Most Valuable Colors
Some individuals believe that the darker the Sapphire the better, while others believe the opposite. However,
very dark Sapphires often appear black and are not very attractive, desirable, or valuable. The darkness can
also be caused by inclusions. An extremely pale Sapphire would be colorless and, although rarer than black
Sapphire, is not particularly attractive or valuable either. Thus, the truth lies between the two extremes.
The most desirable Sapphires are generally those possessing an intense blue color with a great deal of sparkle
and life. These latter two factors are usually helped by high optical clarity and skillful cutting. Ultimately,
which is "best" is a subjective matter, and personal preference is important. As we have said many times throughout
this website, you buy whichever color of gemstone . . . in this case, color of Sapphire you find the most
attractive and most appealing. And . . . there are many stunning colors from which you can choose.
Sapphires - Care and Cleaning
Sapphire Jewelery can be cleaned using hot soapy water, or detergent, rinse thoroughly
afterwards as detergents can cause dermatitis and allergic reactions. Enzyme cleaners should
be avoided for the same reasons. Brushing with an old tooth brush to remove dirt and grease
will also help.
